1. Field of the Invention
The present invention relates to a serial communication apparatus which performs waveform signal serial communication at a predetermined sampling period and also to an image forming apparatus including the serial communication apparatus.
2. Description of the Related Art
An electrophotographic image forming apparatus is known to use a development method which forms an oscillating electric field between a photosensitive drum and a development sleeve of a developing unit to develop an electrostatic latent image on the photosensitive drum by a toner. The toner sufficiently adheres to image portions on the photosensitive drum by a biasing electric field of an oscillating electric field. The toner adhering to non-image portions on the photosensitive drum is separated therefrom by a back-biasing electric field of the oscillating electric field. To form the oscillating electric field, a development voltage composed of a direct-current (DC) voltage and an alternating-current (AC) voltage superimposed thereon is applied to the development sleeve. Japanese Patent Application Laid-Open No. H4-356076 discusses a technique for controlling the ratio of a biasing electric field to a back-biasing electric field to prevent a toner from remaining on non-image portions on a photosensitive drum.
The ratio of the biasing electric field to the back-biasing electric field can be easily controlled by applying a rectangular wave AC voltage to the development sleeve and controlling a duty ratio of high and low levels of the rectangular wave. More specifically, a main control circuit board generates a development AC clock signal representing a period and a duty ratio of the AC voltage applied to the development sleeve and a development AC amplitude control signal representing the amplitude of the AC voltage applied to the development sleeve. The main control circuit board transmits the development AC clock signal and the development AC amplitude control signal to a development high-voltage board. The development high-voltage board applies to the development sleeve the development voltage composed of a DC voltage and an AC voltage superimposed thereon, the AC voltage corresponding to the development AC clock signal and the development AC amplitude control signal.
The main control circuit board of the image forming apparatus also transmits signals to a driver board which operates motors and clutches in the image forming apparatus. Signal lines for transmitting these signals connect the main control circuit board and the driver board and the main control circuit board and the development high-voltage board. With the increase in precision, an operation speed, and functional diversity of the image forming apparatus, the number of signal lines from the main control circuit board is also increasing. Since each circuit board is implemented apart from the main control circuit board in many cases, connecting the main control circuit board and each circuit board with a number of signal lines will not only make it difficult to downsize the image forming apparatus but also degrade the workability at the time of assembly operation of the image forming apparatus.